In radio communication systems, messages (for example, speech, picture information or other data) are transmitted via electromagnetic waves. The electromagnetic waves are transmitted via of antennas, and carrier frequencies which are in the frequency band provided for the respective system.
In addition to the requirement that the dimensions of the antenna must be limited for mobile radio transmitters and receivers, there is also increasingly a requirement for the capability to transmit and receive in different frequency bands. For this reason, there is a requirement for antennas which can be used in a number of frequency bands.
With conventional antennas, such rod antennas (which are used, in particular, in mobile parts), it is impossible to ensure the required coverage of a frequency range which is as wide as possible or of a number of frequency bands, since the impedance and antenna gain of the antenna vary severely as a function of the frequency, so that it is impossible to use the antenna in certain frequency ranges.
Thus, in order to solve this problem, antenna systems have been used until now which include a number of antennas, each of which covers a specific frequency range.
Antenna systems such as these have the disadvantages of the increased space requirement and of suboptimum matching of the antennas to the individual frequencies from the respective frequency band.
DE 19943118 and DE 19919107 each disclose tunable antennas in which the antenna is tuned by adjustment as a function of at least one variable which represents a function of the transmission/reception quality of the radio transmitter/radio receiver (SE).
Systems such as these have the disadvantage that they use mechanically loaded moving elements (adjustment devices) which results in an increased probability of failure.
DE 40 35 766 A1 discloses an electronic controllable antenna with a thin-film structure, in which an insulating material which insulates, for example, a liquid crystal dielectric, which is mounted in a plastic, is enclosed between a base plate and a printed circuit board, in which the relative dielectric constant and/or permeability in the radio-frequency range can be varied corresponding to an electromagnetic field which is applied, and in which the dielectric constant and/or permeability are/is varied via a DC voltage or low-frequency electromagnetic waves, such that impedance matching and a resonant frequency of the antenna can be optimized.
An object to which the present invention is directed is to refine a radio transmitter and receiver such that a virtually constant stable antenna gain is ensured, while covering a wide frequency range.
The radio transmitter and receiver according to the present invention has a first electrically acting antenna body in whose near region a dielectric body is arranged, with the near region referring to the dielectric body being at a distance from the antenna body with respect to wavelengths from a wavelength range which may be used by the mobile radio transmitter and receiver such that the phase delay times which result from that distance do not produce any change to the transmission characteristics in comparison to the desired transmission characteristic. The dielectric body is designed such that its dielectric constant can be varied by at least one control signal, which is produced as an output signal from a closed-loop control device. The control signal is produced by the closed-loop control device until the configuration of this dielectric body results in the dielectric body having a dielectric constant which ensures an optimum value for at least one physical variable, which represents a function of the transmission/reception quality of the radio transmitter and receiver, is detected by a detector and is passed as an input signal to the closed-loop control device, with an optimum value being produced (which can be predetermined or limited, in particular, by the design of the electronic components of the radio transmitter and receiver) when the physical variable which represents a function of the transmission/reception quality of the radio transmitter and receiver allows the conclusion that the transmission/reception quality is a maximum; in particular, in the context of the capability provided by the design.
A major advantage of the mobile radio transmitter and receiver according to the present invention is that the antenna gain is largely stable over a wide frequency range, which is achieved by close-loop control at an optimum value of the variable or variables which represents or represent the reception quality, by varying the dielectric constant of the dielectric body in the near region, that is to say, in the immediate vicinity, of the antenna body, with their being no need to move either the antenna (the antenna body) or the dielectric body, thus reducing the space required and the production costs.
A major advantage of one embodiment is the low-cost implementation of the dielectric body with a variable dielectric constant, since the dielectric constant of ferromagnetic domains on the dielectric body which is coated with them is changed by an external DC voltage field, which can be produced only by application of a DC voltage, using the first layer as one electrical pole and the first electrical antenna body as the second electrical pole, so that only one control signal is required.
Another embodiment allows, firstly, the first layer to be protected against external influences, but it also can fix the first layer, especially if the first layer is an electrolyte. One major advantage of yet another embodiment is the high dielectric constant provided by ceramic, since the frequency range in which the antenna can be tuned and, thus, be used increases in proportion to the magnitude of the dielectric constant of the hollow body that is being used, and the procurement costs are low since ceramic bodies, in particular those provided with ferromagnetic domains, are produced in large quantities, for example as bodies for resonators and capacitors.
A major advantage of a further embodiment is that non-directional external influences are minimized, since these have a greater effect the greater the electrically effective antenna length of an antenna.
Another advantage of an embodiment is that any directional electrical influence on the antenna resulting from the user, in particular his/her head or his/her hands, on the radio transmitter and receiver is minimized, and vice versa.
A major advantage of yet another embodiment is the flexibility and capability to update the implementation of the closed-loop control system, made possible by the use of (closed-loop control) software, as well as the capability to use already existing processors for controlling the mobile radio transmitter and receiver according to the present invention by the use of additional software and/or the adaptation of existing software.
Major advantages of another embodiment are the simple and advantageous implementation of the control unit, and the capability to implement this switching mechanism as an integrated circuit in an upgrade module.
A further embodiment also very largely protects a transmitted or received signal against disturbance influences from the control signal UST.
An advantage of this embodiment is that this makes it possible to use the mobile radio transmitter and receiver in a frequency range in which the ratio of the highest frequency to the lowest frequency is at least 1.5 octaves.
The detection of the forward transmission power level and return transmission power level as a physical variable which represents a function of the transmission/reception quality of the radio transmitter and receiver allows simple implementation of the closed-loop control (matching) for the antenna, since parts which already exist in the radio transmitter and receiver can be used for this purpose.
Moreover, another embodiment of the present invention provides a filter, such as a helix filter, which allows an antenna to be tuned within a wide frequency range without needing to modify the construction of the antenna.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures.